Posture chair



FOSTURE CHAIR l L f fx' y gg o g 26 27 i G `73 45 w56 77 iNVENTO MILTEH F Hmmm. W 'Mw/mm w Mmmm Mmm 3&3? W, BIJEWLU 29E M3937@ PQSTURE CHAIR Filed om. 29, 1955 3 sheets-sheet 5 a 1 i 7? mf v aux/Eamon mmf@ Patented Mar. 15, 1938 tibii'i STATES iiA'iiit FFiih POSTURE CHAIR Application October 29, 1935, Serial No. 47,253

9 Claims.

The present invention relates to an improvement in posture chairs, particularly of the type in which the chair back is tiltably supported and is adapted to be adjusted as to angularity, height 5 and tension, for the purpose of adapting the back to the particular person using the chair.

An object of the invention is to provide a tiltingA structure upon which the `chair back is supported and which is adapted to be tilted against W spring pressure, the arrangement of the tilting axis with respect to the spring and spring connection. with the tilting structure being such that substantial support is provided for the back in the upright position, while, as the chair back V is tilted rearwardly, ihe effort required to tilt the same through a given number of degrees is gradually diminished even though the spring pressure is gradually built up, this eiiort being represented during the initial tilting by rear- 20 ward. pressure exerted by the occupant of the chair as the chair back increasingly tilted, by the rearwardly moving unbalanced Weight of the person seated in the chair, so that throughout all but the initial range or" tilt there is an "5 approximate balancing of the weight of the cccupant oi"v the chair. In tilting back structures heretofore in use there was no compensation for this building 'up oi spring pressure, with the result that, as the chair back was tilted towards Si) its tilting limit, increasingly vgreater eiiort was required to maintain it in tilted position as the angle of tilt approached the limit position, while the initial tilting from the upright position reu quired relatively less elort, and with the result 3^ that either very little support was provided for the back in the uprig--t position if relatively easy tilting was permitted, or if adequate support was provided .in the upright position relatively great effort was required to maintain the 5i-W back in tilted position.

A further object is to provide a structure in which a relatively short spring may be advan tageously used, and which lends itself to compactness, light 'weight and cheapness.y

' Another object is to provide improved adjustment means for adjusting the angle of the chair back with respect to the tilting member, whereby the person seated in the chair may conven- P, iently adjust the handle with very little eiort,

"" and also to provide the handle for operating the angular adjustment means at a convenient location near the edge of the chair seat and at a point forwardly of the chair structure so that its operation will not necessitate a rearward shifting of the persons weight against the chair back. Consequently the adjustment may be made while the back not under tension. To this end it is particularly proposed to provide a universal joint connection between the handle and the adjustment means, whereby the adjustment axis is arranged longitudinally ofthe tilting element while the axis ci the handle may extend at any desired angle thereto, and particularly forwardly and at one side of the swivel post.

A further object is to provide height adjustment means which enables the chair back to be conveniently raised or lowered, and which may be secured in adjusted relation without any possibility of the same becoming accidentally dis placed and at the same time without exerting undue strain upon the parts, and further which permits the adjustment and securing while the user of the chair is seated therein in an upright and natural position. It is also proposed to provide such adjustment means whereby a very secure connection may be produced between the adjustable parts with very little effort on the part of the person making the adjustment. Another object is to provide a back member which may be readily removed for shipping purposes, Without disassembly of any parts.

With the above and other objects in view embodiments of the invention are shown in the accompanying drawings, and these embodiments n will be hereinafter more fully described with reference thereto, and the invention will be iinally pointed out in the claims.

In the drawings:

Fig. l is a side elevation of a chair back tilting mechanism, according tothe invention, the chair base and the upper portion of the chair back being broken away.

Fig. 2 is a longitudinal vertical sectional View.

Fig. 3 is a plan view, the seat being removed, and portions of the spider arms being broken away.

Fig. 4 is a side elevation of a chair back tilting mechanism, according to a modified form` of the invention, a portion of one of the spider arms being broken away.

Fig. 5 is a plan View, partially broken away.

Fig. 5 is a force diagram, according to the invention.

Fig. 7 is another force diagram, according to the invention.

Fig. 8 is a force diagram, according to previously known practice.

Fig. 9 is a perspective view of the tilting member employed in the embodiment illustrated in lgs. l to 3.

Fig. l is a perspective View of the universal joint means employed.

Similar reference characters indicate correspending parts throughout the several gures of the drawings.

Referring to the drawings, and particularly to Figs. l to 3, thereof, the chair seat I0 has secured to its under side a pair of angle-iron spider arms lI-I I, between which there is disposed a bearing member I2, the side portions I3--I3 of which are secured to the respective sides of the spider arms by means of rivets I4. The bearing member I2 is provided with a cylindrical socket I5 in which is engaged the usual post I6 mounted upon the chair base, and upon which the chair seat is thus mounted for swivelling movement.

A tilting bracket member l1 is mounted upon the spider arms rearwardly of the bearing member I2 by means of a bolt I8 extending through holes I9-I9 provided in the sides of the spider arms and through apertured bearing portions -.-2 formed upon the sides of the bracket memloer i1, this bolt being provided at one end with a head 2l, its other end being screw-threaded and engaged by a nut 22. The tilting member I1 is adapted to have limited tilting movement, and for this purpose stops 23-23 are formed upon the outer sides of the bracket member l1 which in the normal non-tilted position abut vertical edge portions 2li- 24, especially formed upon the sides of the spider arms for this purpose. Stops 25--25 are also formed upon the Outer sides of the bracket member I1, their stop surfaces being inclined forwardly and downwardly and adapted in the limit position of rearward tilt to abut the lower edges oi the sides of the angle irons.

A lateral base portion 26 is integrally formed with and extends between the sides of the bracket member l'i and is provided at its rearward end with a downwardly extending flange 21. At the upper side of the base 26 there is provided an upwardly extending wall 28, also integrally formed with and extending between the sides of the bracket member I1, the upper end oi this wall being provided with a slot 29 at each side oi which there are formed rearwardly projecting knife-edge bearing portions 30-30.

The knife edge bearing portions Sli-3d engage V-shape grooves 3I-3I in the head 32?. at one end oi the spring bolt 33, the side Surfaces oi the bolt being preferably ilat adjacent the head, as at 33a, where the bolt is engaged in the slot 29, so that any tendency for the bolt to turn under adjustment of the spring tension is prevented through engagement of said ilat surfaces with the sides of the slot. The bolt extends forwardly in a downwardly inclined direction through an opening 34 provided in a vertically disposed bearing wall portion 35 of the bearing member I2, this portion being integrally formed with and extending between the side portions I3-I3 of the bearing member. At the forward side of the bearing wall 35 there is formed an annular groove Sii in which is seated one end of the spring 31, the other end of the spring being engaged by a washer 38 having an abutment portion 39 which engages the extremity of the spring and forms a seat thereof. The forward end of the bolt 33 is threaded and projects loosely through the washer 38 where it is engaged by an integrally threaded hand wheel or nut :'i, which upon being turned moves the washer 38 toward or away from the wall 35 and adjusts. the tension of the spring.

It will be observed that the point of engagement of the knife-edge bearing portions 30--30 with the spring bolt in the normal non-tilted position is substantially to the rear of the perpendicular distance line from the tilting axis of the bracket member to the line of action oi the spring force, and that the line of action of the spring force intersects the curve through which the spring connection with the bracket member moves. This is clearly shown in the diagram, Fig. 6, in which A represents the tilting axis, B the point of the spring connection with the bracket member, C the curve through which the point B moves, P the line of action of the spring force, and T the torque arm represented by the perpendicular distance between the tilting axis A and the line of spring action P.

By this arrangement the rate of increase of the tension applied to the spring as the tilting member is tilted rearwardly is gradually decreased relatively to equal successive increments of the rearward angular movement, the points B1, B and B3 representing such equal increments of movement and the lines P1, P2 and P3 representing the changes in the line of action of the spring. It will be seen that as the tilting member approaches its limit of tilt the additional tension imparted to the spring for a given angular movement is less than the tension applied during the same angular movement at the beginning of the tilting action, and that the total distance the spring is compressed, represented by the distance B---B3 along the line P3, is substantially less than the total angular movement of the bracket member, represented by the distance B---B3 along the line C. At the same time the torque arm T acting about the axis oi tilt A is gradually decreased, as represented by the lines T1, T2 and T3. As the moment of force is the product of P and T, it will be seen that the successive increases in the spring resistance gradually decrease as the tilting member is tilted rearwardly through equal successive increments of movement, in other words the increase, represented by the difference between the product of Pl and T1 and the product oi P and T, is greater than the increase represented by the difference between the product of P3 and T3 and the product of P2 and T2.

In Fig. 7 there is shown a force diagram similar to that shown in Fig. 6, but on a reduced scale, and showing in addition the reaction or" the persons unbalanced weight against the chair back supported by the tilting member, W representing the effort resulting from rearward pressure and unbalanced weight oi the person and V representing the perpendicular distance between the tilting l axis A and the line of the pressure W. The product or" W and V will equal the product of P and T, and at the rearward limit of tilt the product of "W1 and Vl will equal the product of P3 and T3.

To consider the action in exemplary figures it will be assumed that the initial spring resistance represented by P is 250 pounds, that the radius distance A-B is 2 inches, and the distance A-W represented by the line V l5 inches. The spring is designed to have an increase in resistance of i600 pounds per inch of compression. The limit of tilt of the point B along the curve C represented by the distance B---B3 is 1/2 inch. The

compression distance of the spring shown by the longitudinal movement of the line of spring action from P to P3 is of an inch, so that if P is 250 pounds the increase of P3 over P is 343% pounds giving a total pressure of 593% pounds. The torque arm T is 11/2 inches and the torque arm T3 is 11A inches. The formula P T=W V When reduced to gures will be This means that in the upright or non-tilted position the occupant of the chair will be supported by the tilting arm under 25 pounds pressure. In the fully tilted position the formula P3 T3=W1 V1 when reduced to figures will be Therefore ap-proximately pounds is required in the fully tilted vposition to establish a condition of equilibrium `with the action. of the spring, and as this force is represented bythe approximate unbalanced weight of the average persons body as it is -tilted rearwardly practically no effort is required to maintain the back in tilted position.

The 25 pounds of spring support in the nontilted -position will provide .adequate support for the back in the normal upright working posture, due to the fact that the chair back will not respond in this non-tilted position to the ordinary movements oft-he person in the chair. It will respond however, to the voluntary effort of the person to tilt the chair back rearwardly, and thereupon, as the rearward tilting is increased, the unbalanced weight gradually equalizes the spring pressure and no appreciable effort will be required to maintain the-desired position of tilt.

It may be stated that this is almost the opposite effect from that obtained in ordinary posture chairs, where the line of action of the spring is tangent at the -approximate center of the tilting range to the curve through which the spring connection with the tilting member moves. In this case there is practically no decrease in the rate of increas-eof tension applied to the spring, the distance of the spring compression is approximately the same as the angle of tilt, and there is no appreciable decrease in the torque arm as the tilting member is tilted rearwardly. This is clearly shown by the comparative diagram Fig. 8.

It willbe assumed that the radius of the curve C represented by the line A--B is 2 inches, that the length of the Yline V is l5 inch-es and the pressure W .at the back in the non-tilted position `is 25 pounds, these figures being thesame as in the'diagram Fig. 7. The torque lines T and T3 are each approximately 2 inches vand the distance of compression of the spring represented by the longitudinal movement of the line of action of the spring from P `to P3 is 1/2 inch, this distance beingl equal to the angular distance B-B3 along the curve C. If the spring has an vincrease in resistance of 1000 pounds 'to one inch of compression, as in the diagram Fig. '7, then the increase of resistance for M2 inch of compression will be 500 pounds. The formula W `V=P T when reduced to figures will be W(25) XV(15) =375=P('1871/2) XT(2) This-means that to provide 25 pounds support in the upright or non-tilted position the spring will be adjusted to have an 'initial pressure of 1871/2 pounds. When compressed M2 inch the increase in spring pressure of 500'pounds will make a total pressure of 6871/2 pounds. Thus in the fully tilted position theformula W1 V1=P3 T3 when reduced to figures will be Therefore approximatelyQZ pounds pressure is required in the fully tilted position to maintain the back -in this position, which is considerably more than the unbalanced weight of the person seated in the chair.

Thus in the example, according to the invention, Fig. 7, the difference between 25 and 50 pounds representing the increase in pressure required between the non-tilted position and thel fully tilted position is only 100 per cent, while in the example shown in Fig. 8 the difference, represented by the increase from 25 to 91 pounds, is approximately 26S per cent. Consequently, in these previous structures it has been necessary in order to permit the chair back to be tilted rearwardly with a reasonable amount of ease to sacrifice any substantial support by the spring in the vertical position, so that the ordinary movements of the person seated in the normal upright working position in the chair would cause the chair back to respond by moving rearwardly and the beneficial support that should be ,afforded by the chair back was lost.

A yoke shaped angle adjustment member comprising side portions fil-M and a connecting portion 41a is pivotally mounted between the rearward end portions of the sides of the tilting bracket member ll by means of a cross pin 42 which extends through .apertures 43-43 in the sides and through apertured ears iQ-44 formed upon the upper ends of the side portions :tI-4l.

The connecting portion @la provided in its lower edge with a rectangular cut-out i5 in which is engaged a block 636 having pockets 4l in its ends in which the vertical edges of the cut-out 45 are engaged, the edges of the pockets 4'! being divergent from the center line of the block whereby the portion 4W may have limited tilting movement with respect to the block. A threaded hole 43 is provided through the block which is engaged by a screw shaft 49 journaled in a cylindrical passage 5S provided in the ange portion 2l of the tilting member, said shaft being provided at its inner end beneath the lateral base portion 26 with a U-shaped bracket 5I. A nut 52 is engaged upon the threaded shaft '49 adjacent the outer side of the flange 2l to retain the shaft against relative longitudinal movement. It will be seen that upon rotation of the shaft 49 in one or the other directions the block member 46 is moved either toward or away from the flange 2l and in turn imparts swinging movement to the angle adjustment member about the pin 42.

The sides of the bracket 5l (see Fig. 10) are provided with holes 53-53, which are engaged by lugs 54 provided upon the vertical sides of a rectangular plate 55, provided upon its horizontal sides with lugs 56-56, which engage holes 51-51 of a U-shape bracket member 58 secured upon the end of a shaft 59, journaled in a U-shaped bracket 60 secured upon the base portion 26 by means of a bolt 5i and a nut 62. The axis of the shaft 59 is at an angle of 45 to the axis of the shaft t9, although it may be at any desired angle, and through the universal joint connection between the shaft 59 and the shaft 49, provided by means of brackets 58 and 5I and the plate 55, rotation of the shaft 59 imparts rotation to the shaft 49. This arrangement permits the shaft 59 to extend at one side of and forwardly of the bearing post I2, so that the handle 63 upon the end of the shaft may be located at a convenient point where it may be readily reached by the occupant of the chair for the purpose of adjusting the angle of the back. By placing this handle forwardly, the occupant of the chair, in making the adjustment, will naturally lean forwardly, and therefore rear-ward pressure upon the back will be relieved and the angular adjustment may be made with great ease. In chairs heretofore in use, where the means for angularly adjusting the back Was arranged rearwardly of the chair structure, it was 'customary to lean backwardly in making the adjustment and pressure would therefore be eX- erted upon the back.

The sides 4I-iiI of the angle adjustment member are provided at their rearward marginal portions with V-shape bends (i4-64, which are engaged by the forwardly and inwardly bent flanges fiii provided upon a height adjustment member et. A strap member 61 is riveted to the member 66 and extends at each side thereof where it is provi-ded upon its ends with the vertical posts 68--58 upon the upper ends of which there is supported the back member 69, a portion of which is shown in Fig. 3. In one of the side portions di there is provided a threaded bearing hole 1S, the axis of which is at an inclined angle to the piane of said portion 4|, the metal about the bearing being embossed, as at 'I I, to bring said axis into this relation.

A threaded shaft 12 is engaged in the bearing hole lil, and at its inner end is provided with a tapered wedge portion 13, which engages in the acute angle corner formed by the outer flange of the V-shape portion '64, at the opposed side of the angle adjustment member from the bearing portion 1i), and the inner surface of the height adjustment member 56. A handle 14 is provided upon the end of the shaft 12 which is disposed in a convenient location where it may be conveniently turned by the person occupying the chair. The wedge portion 'I3 has bearing in an apertured bracket member 15 secured to the side portion 4I. The height adjustment member is provided near its upper and lower ends with stop lugs 16 and 'i1 in the path of the wedge portion I3, and which limit the extent to which the height adjustment member may be adjusted and at the same time prevent its accidental removal. The bracket 15 supports the inner end of the shaft 12 against any tendency to bend, in the event that the height adjustment member is a1- lowed to drop, bringing the stop lug 16 forcibly against the inner end of the shaft, and such as might occur when the shaft 12 is turned outwardly to loosen the connection of the height adjustment member with the angle a-djustment member.

The angle adjustment member is preferably formed of sheet metal, so that the sides thereof are slightly springy, and, when the shaft 12 is turned outwardly to withdraw the tapered wedge end 13 from wedging engagement between the angle adjustment member and the height adjustment member, the sides il-4i contract slightly with respect to the flanges E5-65 so that they are relatively loose with respect to the latter. The strap member 51 may thereupon be grasped at each side and easily raised or lowered as desired to adjust the height of the back.

l Thereupon the adjustment is fixed by turning shaft 'i2 inwardly causing the tapered wedge portion 13 to tightly wedge between the flange of the V-shape portion S4 at one side and the inner surface of the height adjustment member B. At the same time the flange of the V-shape portion 54 at the other side is tightly pressed against the flange t5 of the height adjustment member through the outward spreading pressure exerted upon the side portion 4I as the tapered wedge portion 13 is forced into place. The result of this is that in the adjusted position there is a tight engagement established between the anges of the angular adjustment member and the flanges of the height adjustment member along the entire surfaces of the flanges of the angular adjustment member, and therefore an absolutely rigid relation is established, and this with very little effort required in the turning of the shaft 12 to establish this relation. In order to remove the back, for shipping purposes, it is only necessary to Withdraw the shaft 12 to a point where the tapered wedge end 13 is out of the path of the stops 16-16, whereupon the height adjustment member 66 may be slipped off the angle adjustment member.

In Figs. 4 and 5, I have illustrated a modified form of the invention, in which the tilting member is formed of sheet metal and is mounted for tilting movement upon the bearing post I2, instead of upon the sides of the spider arms, as in the first embodiment. The sheet metal tilting bracket member comprises an upper transverse portion 8D and side portions 8I-8I bent downwardly at right angles therefrom, the side portions being provided at their rearward upper corners with apertured portions 82--82 in which the pivot pin 42 pivotally mounting the angle adjustment member is engaged.

The tilting member is mounted for tilting movement at the forward lower corners of the side portions by means of a bolt 83 engaged through apertured bearing lugs 84--84 formed upon the bearing post I2, the sides 8I-8I being disposed between these bearing lugs 84-84 and the side portions I3-I3 of the bearing post, which are secured to the angle iron spider arms Il-II by means of rivets I4. The sides 8I--8l of the tilting member are provided with lanced and outwardly embossed stop portions 85 and 86 between which are disposed the inner head ends of the rearwardly disposed rivets I4-I4, and which hea-d ends act as limit stops for determining the degree of tilting movement of the tilting member, the stop portions 86 being engaged with the rivet heads in the non-tilted position and the stop portions 85-85 engaging the rivet heads in the fully tilted position.

In the transverse top portion 80 there is provided toward its forward edge a cross-shaped opening 81, having lugs 88 bent upwardly from its transverse portion and disposed at each side of its longitudinal portion, the rearward surfaces of these lugs forming with the upper surface of the top portion 80 V-shaped pockets in which are engaged the knife edge portions 89-89 of the head 90 provided upon the end of the spring bolt 33, which bolt extends through the longitudinal portion of the opening 81.

A sheet metal plate 9I is disposed within the lower portion of the tilting member between the sides 8I-8I, and is secured to said sides by means of lugs 92 formed upon its side edges and engaged and staked into apertures 93 formed in the sides 8I-8I, this plate being provided at its rearward end with a downwardly bent apertured flange 94 in which is supported the angle adjusting screw shaft 49. The shaft 59 for operating the screw shaft 49 is mounted at the under side of the plate 9| in a similar manner to the mounting of the operating shaft 59 upon the under side of the base portion 26 in the irst embodiment. Inasmuch as the angle adjusting and height adjusting parts are substantially identical to those of the first embodiment a further description of these is not deemed necessary.

Eil

I have illustrated and described preferred and satisfactory embodiments of the invention, but it will be understood that changes may be made therein, within the spirit and scope thereof, as defined in the appended claims.

Having thus described my invention what I claim and desire to secure by Letters Patent is:-

1. In a back support for use in a chair, a chair back supporting member having a pair of spaced side portions, a vertically adjustabie chair back member having a pair of spaced flanges engaged for vertical sliding movement with the outer sides of said side portions, and a screw shaft mounted in one of said members having a wedge end adapted to engage between one of said side portions and said back member to press said side portion tightly against one of said anges.

2, In a back support for use in a chair, a chair back supporting member having a pair of spaced side portions, a vertically adjustable chair back member having a pair of spaced flanges engaged for vertical sliding movement with the outer sides of said side portions, and a screw shaft having threaded engagement in one of said side portions and having a wedge end adapted to engage between the other side portion and said back member to press said other side portion tightly against the adjacent flange, the other side portion adapted through said threaded engagement of said screw shaft therewith to be tightly pressed against said other flange.

3. In a back support for use in a chair, a substantially U-shaped chair back supporting member having a transverse portion and a pair of spaced rearwardly extending side portions, a vertically adjustable chair back member rearwardly of said supporting member having a pair of spaced flanges engaged for vertical sliding movement with the outer sides of said side portions, a screw shaft having threaded engagement in one of said side portions and having a Wedge end adapted to engage between the other side portion and said back member to press said side portion tightly against one of said flanges, the other side portion adapted through said threaded engagement of said screw shaft therewith to be tightly pressed against said other flange.

4. In a back support for use in a chair, a chair back supporting member having a pair of spaced side portions, a vertically adjustable chair back member having a pair of spaced flanges engaged for vertical sliding movement with the outer sides of said side portions, one of said side portions having an inclined inner surface adjacent the inner surface of said back member, a screw shaft having threaded engagement in the other of said side portions and having a wedge end adapted to engage between said inclined inner surface and the inner surface of said back member to vpress said first side portion tightly against one of said anges, the other side portion adapted through said threaded engagement of said screw shaft therewith to be tightly pressed against said other ange.

5. In a back support for use in a chair, a chair back supporting member having a pair of spaced side portions having outwardly diverging anges at their rearward edges, a chair back member having a pair of spaced inwardly converging flanges engaged with the outer sides of said diverging flanges of said side portions, a screw shaft having threaded engagement in one of said side portions and having a wedge end adapted to engage between the diverging flange of the other side portion and said back member to press said flange tightly against the adjacent flange of said back portion, the flange of the other side portion adapted through said threaded engagement of said screw shaft therewith to be tightly pressed against said other flange of said back portion.

6. In a back support for use in a chair, a chair back supporting member, a chair back member engaged with said supporting member for vertical sliding movement, a screw shaft mounted in one of said members having a locking end arranged to engage between said members to secure the back member in adjusted position, a pair of vertically spaced stop means on another of said members normally in the path of the locking end of said screw shaft to limit the relative vertical movement of said back member, said back member adapted to be removed from said supporting member upon retraction of said screw shaft to remove said locking end out of the path of said stop means.

7. In a chair, a post having spaced side portions, spider arms at the outer sides of said spaced side portions, headed rivets engaged through and securing said side portions and spider arms together, the rivet heads projecting inwardly from the inner surfaces of said side portions to form stop abutments, bearing means on said post, a tilting chair back supporting member mounted on said bearing means for tilting movement about a horizontal axis and comprising side portions inwardly spaced from said side portions of said post in opposed relation to said rivet heads, a pair of outwardly projecting stop portions on each of said side portions of said tilting member respectively disposed forwardly and rearwardly in the path of said rivet heads and adapted to engage said rivet heads' respectively in the tilted and non-tilted positions of said tilting member, and spring means acting between said post and said tilting member to normally maintain said tilting member in non-tilted position.

8. In a tilting chair back support for use in a chair having a seat element, a bracket member mounted upon said seat element, a chair back supporting angle adjusting member hingedly connected to said bracket member having a transverse portion having a vertically sided slot open at one end, a rotatable screw carried by said bracket member, a nut engaged upon said screw, slot means in the sides of said nut pivotally engaging the vertical sides of said slot of said angle adjusting member whereby rotation of said screw i imparts swinging movement to said angle adjusting member relatively to said bracket member, and means for rotating said screw.

9. In a tilting chair back support for use in a chair having a seat element, a bracket member mounted upon said seat element, a chair back supporting angle adjusting member hingedly connected to said bracket member having a transverse portion having a vertically sided slot open at one end, a block member having slot means in its sides pivotally engaging the vertical sides of said slot of said angle adjusting member, means connected to said bracket member engaging said block member and operative to adjustably move said block member whereby swinging movement is imparted to said angle adjusting member relatively to said bracket member.

WALTER F. HEROLD. 

